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    Re: Index Correction
    From: Doug Royer
    Date: 2007 May 4, 10:42 -0700




    General question to the list:


    It is common practice to check for IC before and after a round of sights. In my experience, they are seldom the same particularly when taking sights under non-standard temperatures.


    Question: what correction would you apply?  Generally what I do is a combination of fudging and black magic but it usually entails simply taking the two ICs and averaging them to arrive at a single IC that can be applied to the entire round of sights.


    Please: I am not looking for involved statistical computations. I am trying to determine what other navigators do in the field/at sea.





    Well Robert, this is what I usually do for a round of sights.

    Check the index error at some point before the round or single sight begins. The closer to the time of cuts the better. Then take the sights needed in the round and apply the correction. Some sextants are more prone than others to shifts in index error caused by environmental conditions in my experience. Over time of using a certain sextant one gets a “feel” for knowing when to be especially concerned or vigilant about checking for a more than “normal” increase in the sextant’s error. Not very scientific but just something I’ve learned from experience. My Tamaya holds it’s error fairly steady over a wide range of temps and humidity over many years.

    Close enough for gubment work so to speak.

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